A cyclopean neural mechanism compensating for optical differences between the eyes

Abstract

The two eyes of an individual routinely differ in their optical and neural properties, yet percepts through either eye remain more similar than predicted by these differences. Little is known as to how the brain resolves this conflicting information. Differences in visual inputs from the two eyes have been studied extensively in the context of binocular vision and rivalry [1], but it remains unknown how the visual system calibrates and corrects for normal variability in image quality between the eyes, and whether this correction is applied to each eye separately or after their signals have converged. To test this, we used adaptive optics to control and manipulate the blur projected on each retina, and then compared judgments of image focus through either eye and how these judgments were biased by adapting to different levels of blur. Despite significant interocular differences in the magnitude of optical blur, the blur level that appeared best focused was the same through both eyes, and corresponded to the ocular blur of the less aberrated eye. Moreover, for both eyes, blur aftereffects depended on whether the adapting blur was stronger or weaker than the native blur of the better eye, with no aftereffect when the blur equaled the aberrations of the better eye. Our results indicate that the neural calibration for the perception of image focus reflects a single 'cyclopean' site that is set monocularly by the eye with better optical quality. Consequently, what people regard as 'best-focused' matches the blur encountered through the eye with better optics, even when judging the world through the eye with poorer optics.

Figure 1. Neural compensation of interocular differences in blur magnitude

(A) Wavefront maps and corresponding PSFs in both eyes of a subject (S1). (B,C) Illustration of Experiments 1 and 2. (D) Differences in the magnitude of retinal image blur between the left and right eyes of 12 observers. (E) The magnitude of retinal blur that appears best-focused to each observer is the same through either eye and closely corresponds to the blur in the better eye. (F) Adaptation to different blur levels is the same within each eye and is neutralized when the blur magnitude equals the blur of the better eye (indicated with arrow).